NAME¶

std::numpunct - std::numpunct

Synopsis¶

Defined in header <locale>
template< class CharT >
class numpunct;

The facet std::numpunct encapsulates numeric punctuation preferences. Stream I/O
operations use std::numpunct through std::num_get and std::num_put for parsing
numeric input and formatting numeric output.

The numbers that are supported by std::numpunct have the format described below.
Here digit represents the radix set specified by the fmtflags argument value,
thousands-sep and decimal-point are the results of thousands_sep() and
decimal_point() functions respectively. The format of integer values is as follows:

integer ::= [sign] units
sign ::= plusminus
plusminus ::= '+' | '-'
units ::= digits [thousands-sep units]
digits ::= digit [digits]

The number of digits between the thousand-seps (maximum size of digits) is specified
by the result of grouping().

The format of floating-point values is as follows:

floatval ::= [sign] units [decimal-point [digits]] [e [sign] digits] |
[sign] decimal-point digits [e [sign] digits]
e ::= 'e' | 'E'

std-numpunct-inheritance.svg

Inheritance diagram

Specializations¶

The standard library is guaranteed to provide the following specializations (they
are required to be implemented by any locale object):

Defined in header <locale>
std::numpunct<char> provides equivalents of the "C" locale preferences
std::numpunct<wchar_t> provides wide character equivalents of the "C" locale
preferences

Member types¶

Member type Definition
char_type CharT
string_type std::basic_string<CharT>

Member functions¶

constructor constructs a new numpunct facet
(public member function)
destructor destructs a numpunct facet
(protected member function)
decimal_point invokes do_decimal_point
(public member function)
thousands_sep invokes do_thousands_sep
(public member function)
grouping invokes do_grouping
(public member function)
truename invokes do_truename or do_falsename
falsename (public member function)

Protected member functions¶

do_decimal_point provides the character to use as decimal point
[virtual] (virtual protected member function)
do_thousands_sep provides the character to use as thousands separator
[virtual] (virtual protected member function)
do_grouping provides the numbers of digits between each pair of thousands
[virtual] separators
(virtual protected member function)
do_truename provides the string to use as the name of the boolean true and
do_falsename false
[virtual] (virtual protected member function)

Member objects¶

static std::locale::id id id of the locale
(public member object)

Example¶

The following example changes the string representations of true and false:

// Run this code

#include <iostream>
#include <locale>

struct french_bool : std::numpunct<char>
{
string_type do_truename() const override { return "vrai"; }
string_type do_falsename() const override { return "faux"; }
};

int main()
{
std::cout << "default locale: "
<< std::boolalpha << true << ", " << false << '\n';
std::cout.imbue(std::locale(std::cout.getloc(), new french_bool));
std::cout << "locale with modified numpunct: "
<< std::boolalpha << true << ", " << false << '\n';
}

Output:¶

default locale: true, false
locale with modified numpunct: vrai, faux

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 338 C++98 the sign token allowed an optional removed the whitespace
whitespace following + or -

See also¶

numpunct_byname creates a numpunct facet for the named locale
(class template)